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at 30-40 turns per minute for half an hour at a temperature of 17-5°, and
immediately afterwards filtered.

In a cylindrical beaker, 50 c.c. of the filtrate ( = 0-5 gram of substance)
are heated on a water-bath at 65° for 15 minutes with 80-100 c.c. of the
molybdic solution (6). When cool, the mixture is filtered and the ammonium
phosphomolybdate washed with i% nitric acid and dissolved in about 100
c.c. of 2% ammonia ; after addition of 15 c.c. of magnesia mixture (c) and
shaking, the procedure is as in the determination of the total phosphoric
anhydride (see p. 123).

3.  Free Lime.—10 grams of the slag are treated with about 250 c.c.
of water in a 500 c.c. measuring flask, with frequent shaking over several
hours.    When the volume has been made up with water and the liquid
mixed and filtered, 50 or 100 c.c. (= i or 2 grams of substance) are titrated
with N/2-hydrochloric acid and phenolphthalein.    i c.c. N/2-HC1 = 0-014
gram CaO.

4.  Degree of Fineness.—50 grams of the slag as received are sieved
for 15 minutes with a No. 100 Kahl sieve 20 cm. in diameter.   The weight
remaining in the sieve is subtracted from 50 grams and the remainder multi-
plied by 2 to give the percentage of fine slag.

5.  Specific Gravity.-—-This is determined with an ordinary picnometer,
alcohol or essence of turpentine being used as the liquid.

6.  Adulterations.—Thomas slag is adulterated with mineral phosphates,
aluminium phosphate or Redonda phosphate,  Martin slag, Wolter and
Wiborg phosphates (artificial slags) and coal dust.

For detecting natural phosphates and aluminium phosphate, recourse
may be had to microscopic examination, to determinations of the specific
gravity, of the loss on ignition and of the portion soluble in hot water and
to tests for fluorine, carbonates and alumina (the slag is shaken in the cold
with sodium hydroxide solution and the liquid filtered, acidified with hydro-
chloric acid and tested with ammonia).

Martin slag and Wolter and Wiborg phosphates are indistinguishable
from the Thomas slag, but in general are less rich in phosphoric anhydm|^

Coal dust may be observed under a lens or by shaking the slag
water (the coal floats).

* *


Genuine Thomas slag contains 11-23% °f "total P2O5 (on the average ^>^.t
I7%) ancl 9'5~I6% of P2O6 soluble in citric acid (on the average, 12 -5-1 ^5%).
It contains also 41-52% of total CaO (mean, 46-47%), 3-6% MgO, 9-2 *%" of
ferroso-ferric oxide (mean, about 15), 3-8% SiO2 (mean, about 7), and &b.out
10% of matter soluble in hot water. It contains only very small quantities' of
alumina and no fluorine, and on calcination loses not more than i % of its weight.
Its specific gravity is 3-3-3, and under the microscope it is seen to be comp^SL* of
small, yellowish, acute-angled splinters.

As regards the testing of the genuineness of mineral phosphates, it
borne in mind that, unlike Thomas  slag, these do not contain P2O5 solpibl® int
citric acid, and are almost entirely insoluble in hot water ; on ignition,
considerably in weight  (water,  CO 2) ;   they contain fluorine ;   their
gravities are below 3, and under the microscope they are seen to consist o
ish granules.    Redonda phosphate is detected by testing for aluminium (a
precipitate in test 6).



 Mineral Phosphates " (ibid., 1897, p. 663); G. Masoni: " Contribution to^me